Assumption was founded by German farmers in 1876. The first church, completed the same year, was called “St. Valentine,” after the patron saint of one of the founding families. When the first church was destroyed in 1886 by a fire caused by lightning, the church was rebuilt and dedicated to the Blessed Virgin Mary of the Assumption. The care of the parish was entrusted first to the
Benedictine Fathers and later to the Oblates of Mary Immaculate.

After World War II, the community rapidly outgrew the church in which they had worshiped for so long. A new church and expanded campus were completed in 1954 and expanded still further in 1963. Over the years, with the changing demographics of the area, Assumption has continued to adapt. In 1994, the parish school, which had operated since 1887, consolidated with those of St. Richard and St. Peter in Richfield to form Blessed Trinity Catholic School. In 2001, Assumption expanded its ministries by offering them in both English and Spanish. In 2020, the three parishes in Richfield began to collaborate even more closely. While they remain three distinct parishes, they have one pastor, one parish staff, one set of bilingual ministries, and one mission to spread the Gospel.